Process for preparing rubber-modified styrene resins

A process for preparing rubber-modified styrene resins with excellent impact resistance which comprises:

• preheating in a complete mixing tank, under conditions sufficient to support up to 10% conversion and under conditions prevailing prior to rubber phase inversion, a feed formulated from:
• 100 parts by weight of reactants consisting of:
• 98 to 88% by weight of styrene-monomer, and
• 2 to 12% by weight of a high-viscosity rubber including polybutadiene and styrene-butadiene copolymer, wherein said rubber has a viscosity of 500 to 2,000 centipoises, wherein this viscosity is measured in a 5% by weight solution in styrene at 25.degree. C.,
• 0.01 by 0.2 part by weight of an inert organic solvent;
• converting up to 10% of said monomer during said preheating to form a preheated feed comprising a continuous phase of said rubber dissolved in said monomer and a discontinuous phase of polymer particles;;
• continuously supplying said preheated feed to one end of first reaction zone consisting of a plug flow tower equipped with an agitator or a plurality of such reaction zones connected in series;
• effecting preliminary polymerization, in said first reaction zone with agitation, of said preheated feed to a conversion sufficient for transformation of said continuous phase of rubber dissolved in said monomer and discontinuous phase of polymer particles into a discontinuous phase of rubber dissolved in said monomer in a continuous phase of said polymer;
• controlling the conditions of preliminary polymerization in said first reaction zone effective to cause rubber phase inversion and to limit the weight average particle diameter of said rubber particles in said reaction zone to 0.8 to 5 .mu.m to thereby form a prepolymerized product;
• withdrawing said prepolymerized product, comprising said discontinuous phase of rubber and unconverted styrene monomer in said continuous phase comprising said styrene polymer, from another end of said reaction zone different from the feed end thereof;
• supplying said prepolymerized product to a following plug flow reaction zone, that includes static mixing means therein;
• increasing conversion of said prepolymerized product within said following plug flow type reaction zone;
• and
• recovering rubber modified styrene resin from said following plug flow reaction zone.